Besides, moving on would be a terrible military decision. She needs a substantially bigger army to take on Westeros, and nobody is just going to give it to her. She's creating a Khalasaar of people who love her. There was really no other reasonable option than to turn to the nearest city after Astapor.

I suspect she will eventually unite the Dothraki as well, but may not. I hope so. I want her to create the greatest army the world has ever seen. After that, I'm not sure what I think should happen with her, but she needs to be when a Habsburg meets a Genghis meets a Roosevelt with the heart of a Mother Teresa